Ultrathin Transparent B-C-N Layers Grown on Titanium Substrates with Excellent Electrocatalytic Activity for the Oxygen Evolution Reaction

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Energy Materials, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/acsaem.9b02339Ultrathin B-C-N layers grown on Ti substrates are investigated as efficient anodes for electrochemical water splitting. A fast and direct synthetic route has been used based on plasma-enhanced chemical vapor deposition with methylamine borane as a single-source molecular precursor. The effect of growth time on the morphological and structural properties and on the chemical composition of the layers has been investigated by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy coupled with electron energy loss spectroscopy. Flat B-C-N layers on top of an amorphous titanium oxide layer present at the Ti surface have been obtained by using short growth times, while longer growth times give rise to core/shell structures formed by vertical wall B-C-N layers and titanium carbonitride phases. The obtained layers present enhanced electrocatalytic activity for the oxygen evolution reaction in alkaline aqueous solutions. Moreover, because of their ultrathin nature, the B-C-N layers preserve the photocurrents of the underlying titanium oxide layer, acting as transparent electrodes with high conductivity for the photogenerated charge carriers and improved electrocatalytic activity for the oxidation of water to oxygen gasThis work has been funded under RTI2018-099794-B-I00 grant of Spanish MICINN and by PRIN Grant FERMAT (2017KFY7XF) of Italian MIU

MoS2 photoelectrodes for hydrogen production: Tuning the S-vacancy content in highly homogeneous ultrathin nanocrystals

Tuning the electrocatalytic properties of MoS2 layers can be achieved through different paths, such as reducing their thickness, creating edges in the MoS2 flakes, and introducing S-vacancies. We combine these three approaches by growing MoS2 electrodes by using a special salt-assisted chemical vapor deposition (CVD) method. This procedure allows the growth of ultrathin MoS2 nanocrystals (1-3 layers thick and a few nanometers wide), as evidenced by atomic force microscopy and scanning tunneling microscopy. This morphology of the MoS2 layers at the nanoscale induces some specific features in the Raman and photoluminescence spectra compared to exfoliated or microcrystalline MoS2 layers. Moreover, the S-vacancy content in the layers can be tuned during CVD growth by using Ar/H2 mixtures as a carrier gas. Detailed optical microtransmittance and microreflectance spectroscopies, micro-Raman, and X-ray photoelectron spectroscopy measurements with sub-millimeter spatial resolution show that the obtained samples present an excellent homogeneity over areas in the cm2 range. The electrochemical and photoelectrochemical properties of these MoS2 layers were investigated using electrodes with relatively large areas (0.8 cm2). The prepared MoS2 cathodes show outstanding Faradaic efficiencies as well as long-term stability in acidic solutions. In addition, we demonstrate that there is an optimal number of S-vacancies to improve the electrochemical and photoelectrochemical performances of MoS2PID2021-126098OB-I00, PID2020-116619GA-C22, TED2021-131788A-I00, SI3/PJI/2021-0050